The overall purpose of this project is to investigate in detail the mechanism of regulation of adenylate cyclase (the enzyme that catalyzes the synthesis of cyclic AMP) activity associated with membranes isolated from brain. The basic hypothesis underlying this work is that there are two forms of adenylate cyclase; one form is active, the other is inactive. The interconversions between the two forms probably occur by separate reactions. Preliminary investigations have shown that activation of adenylate cyclase is temperature and time dependent. It is dependent upon one or more divalent cations and requires a protein co-factor which is bound to the membrane. Inactivation may be inhibited by fluoride ions. The specific goal of this project will be to investigate the nature of these reactions and to identify the specific co-factors required. It is possible that these reactions are catalyzed by enzymes. If so, these enzymes will be isolated, purified, and characterized.